1. Field of the Invention
The present invention concerns an internal combustion engine and a method of operating an internal combustion engine in which excessive mechanical loadings and/or wear are avoided by skip firing.
The individual combustion chambers of the internal combustion engine are in the form of piston-cylinder units (for brevity, often referred to as the cylinders). Depending on the respective type of internal combustion engine, the combustion chambers can be subdivided into prechambers and main combustion chambers. In that case, the ignition device is generally associated with the prechamber.
For various reasons, it may be desirable for cylinders of the internal combustion engine to be at least temporarily selectively shut down or deactivated, which in the context of the present application is to be interpreted as meaning that the respective ignition device and/or the device for introducing fuel remains inactive.
2. Description of the Related Art
Methods of cylinder deactivation, referred to as ‘skip firing’, are known from the state of the art. Skip firing is used predominantly in larger engines with more than six cylinders in order to reduce the fuel consumption and emissions when there is a reduced demand for power.
DE 43 10 261, for example, describes that patterns for selective skip firing (referred to in the specification as deactivation patterns) can be predetermined to protect an engine from overloading. The patterns are advantageously matched to the number of cylinders such that there are circulating deactivation sequences, that is to say, each cylinder is relieved of load within a very short time.
It is further known from DE 2928075 that the sequence of commands for ignition and for skip firing is selected such that the internal combustion engine runs as smoothly as possible, and in particular, harmonics of the resonance frequencies of the engine suspension and the drivetrain are avoided.
US 2013/0289853 describes a method of skip firing, wherein ignition commands are stored in a reference table (referred to as the look-up table) and the entry for the next ignition command is determined by means of a counter in the look-up table.